It has long been known to manufacture and distribute PSA stock for labels by providing a layer of face or facestock material for the label or sign backed by a layer of a PSA which in turn is covered by a release liner or carrier. The liner or carrier protects the adhesive during shipment and storage and allows for efficient handling of an array of individual labels after the labels are die-cut and the matrix is stripped from the layer of facestock material and up to the point where the individual labels are dispensed in sequence on a labeling line. During the time from die-cutting to dispensing, the liner or carrier remains uncut and may be rolled and unrolled for storage, transit and deployment of the array of individual labels carried thereon.
Failure to reliably dispense is typically characterized by the label following the carrier around a peel plate without dispensing or "standing-off" from the carrier for application to the substrate. Such failure to dispense is believed to be associated with excessive release values between the label facestock material and the liner. Dispensibility also is dependent upon the stiffness of the facestock. Failure to dispense may also be characterized by the wrinkling of the label due to lack of label stiffness at the dispensing speed as it is transferred from the carrier to the substrate. Another particular need in many labeling applications is the ability to apply polymeric-film labels at high line speeds, since an increase in line speed has obvious cost saving advantages.
In many label applications, it is desirable that the facestock material be a film of polymeric material which can provide properties lacking in paper, such as clarity, durability, strength, water-resistance, abrasion-resistance, gloss and other properties. It is desirable to reduce the thickness or "down-gauge" the facestock material in order to attain savings in material costs. Such reduction in facestock thickness often has resulted in reduced stiffness and the inability to die-cut and dispense the labels in a reliable commercially acceptable manner using automatic machinery.
A problem with these thin polymeric facestocks is that it is difficult to predict their die-cutting characteristics. Good die-cutting requires that the die cuts through the facestock and adhesive, but stops short of the silicone-coated release liner. Incomplete or poor die-cutting results in the labels failing to separate from the waste matrix material during subsequent separating of the matrix. Overcutting (i.e., heavy die strike on the liner or deep cut into the liner) creates problems during high speed dispensing. These problems include labels going around the peel tip assembly with the liner, or liner breakage due to the weakness induced by the die cutting partially into the liner.
There are two generally accepted techniques for measuring die-cuttability. One of these techniques involves using a multilevel die with different blade cutting depths and combinations of different bearer-anvil compressive forces. The die-cuttability of the PSA construction is determined by noting the minimum blade cutting depth or minimum compressive force needed for a non-fuzzy, clean, die-cut edge. The other technique involves manually separating and visually observing a die-cut sample against the light. Good die-cuttability is indicated by an easy and clean removal of the label from the matrix. The edge of a separated label exhibiting good die-cut characteristics looks clean and does not show signs of a roughened edge, fuzziness and stretching, or tickers hanging on the die-cut edge. Both of these methods are costly, time consuming, nonquantitative and operator subjective.
The present invention eliminates these shortcomings by employing a quick, reliable and quantitative test for selecting facestock materials by providing an accurate prediction of the die-cutting characteristics of such facestock materials. The test used with the inventive method provides a single number or value for measuring die-cuttability, this number being referred to as the friction energy required to separate the waste matrix from die-cut shapes cut in the facestock material. This test can be conducted in a laboratory using laboratory-size, die-cutting apparatus and relatively small test samples. The inventive method is useful in selecting facestock materials for use in making PSA constructions as well as in selecting other substrates that are to be subjected to cutting operations. The method is particularly suitable for selecting relatively thin facestock materials that are difficult to die-cut.
The substrate selection method of the invention eliminates the need to manufacture large master rolls of material for testing of die cutting, instead requiring only hand-sheet samples. This represents a significant savings of time and money, e.g., by avoiding scrap during testing. The selection method provides a means for generating quantitative data on sheet material cutting characteristics in an efficient, economical manner.